Rifle barrel electroplating fixture

ABSTRACT

A tool adapted to insure concentricity between an electroplating anode and the bore of a small bore rifle, the tool comprises a chamber-anode-position, a muzzle cap, and a muzzle-anode-positioner acting in concert to locate the anode in the center of the bore.

1972 A. J. WILLIAMS 7 IFLE BARREL ELECTROPLATING FIXTURE Filed Oct. 51, 1969 flfiaz- ATTORNEY Patented Feb. 29, 1972 3,645,881 RIFLE BARREL ELECTROPLATING FIXTURE Alfred J. Williams, Berkley, Mich., assignor to General Motors Corporation, Detroit, Mich. Filed Oct. 31, 1969, Ser. No. 872,804 Int. Cl. B01k 3/04; C23b 5/70, 5/56 US. Cl. 204286 2 Claims ABSTRACT OF THE DISCLOSURE A tool adapted to insure concentricity between an electroplating anode and the bore of a small bore rifle, the tool comprises a chamber-anode-positioner, a muzzle cap, and a muzzle-anode-positioner acting in concert to locate the anode in the center of the bore.

This invention relates to electroplating (e.g., chromium) the bore and chamber of a small bore rifle barrel. A small bore rifle barrel is considered to be one of 30 caliber or less. It is known to apply corrosion and wear resistant chromium coatings to the chambers and bores of rifle barrels. Coatings of no more than 0.001 inch are effective to provide the requisite protection. To provide a uniform coating of chromium on the internal surface of a small bore rifle barrel concentricity between the anode and the bore should be within about 0.002 inch or less for 30 caliber rifles and considerably less (i.e., less than about 0.001 inch) for smaller calibers such as the 22 or 25 caliber rifles.

It is an object of this invention to provide a tool for centering the anode in the bore of a small caliber rifle barrel especially a barrel whose outside diameter varies (e.g., tapers) along its length such that the muzzle end has a smaller diameter than the chamber end and other sections of the barrel intermediate the chamber and muzzle end.

This and other objects of this invention will become apparent from the detailed description which follows.

FIG. 1 shows a partially sectioned, elevational view of the tool of this invention.

FIG. 2 shows an enlarged, broken, sectioned, elevational view of the chamber-anode-positioner, muzzle cap, and muzzle-anode-positioner of this invention.

In the figures there is shown a rifle barrel 2 having a bore 3, a chamber 4 and a muzzle 6. The barrel 2 generally tapers from the chamber end to the muzzle end. The barrel 2 is for use with a semi-automatic, gas operated rifle and accordingly includes a gas port 8. The gas port 8 is located intermediate the muzzle 6 and the chamber 4 through an enlarged section 10. In this embodiment, the enlarged section 10 is machined concentrically to the bore 3 and serves as the mounting location for the rifles front sight ,(not shown). A barrel extension 12, having a flange 42, screws onto a threaded portion of the barrels chamber end 4. The barrel extension 12 has an internally splined portion 32 adapted to receive a portion of the balance of the operating mechanism of the rifle. The barrel extension 12 is not plated and an appropriate plater stop-off is used to mask it during plating.

A chamber-anode-positioner 14 is fitted to the chamber end 4 of the barrel 2. The chamber-anode-positioner comprises a sleeve 16 which has a bore therethrough. A first portion 18 of the bore in the sleeve 16 has a small internal diameter which is about equal to the outside diameter of the barrel around the chamber 4 so that a slip fit is possible. A second portion 20 of the bore in the sleeve 16 has a larger internal diameter. A shoulder 40 is formed where the two portions 18 and 20 meet in the sleeve 16.

The chamber-anode-positioner is placed about the chamber 4 and the barrel extension 12. The flange 42 on the barrel extension 12 rests on the shoulder 40 and is held there by means of dog-nosed screws 30. Electrolyte ports (e.g., outlets) 22 are located in the second portion 20 of the sleeve 16. In operation the ports 22 are maintained at or slightly above the electrolyte level 66 in a plating tank.

A plug 24 is in the end of the sleeve 16. The plug 24, carries and centers the anode 26 in the chamber 4. The plug 24, in this case, comprises an electrical insulator such as nylon or Teflon. An anode electrical lead 28 is attached to the anode 26 in any convenient manner. A hook 68 is provided to hang the assembly in an electroplating tank.

At the muzzle end 6 of the barrel 2 there is provided a muzzle-anode-positioner 37. The muzzle-anode-positioner 37 comprises a sleeve 38 having an internal diameter 39 so sized as to closely slip over the outside diameter of the enlarged section 10. A hollow cylindrical muzzle cap 46 is appropriately fixed (i.e., screwed) to the muzzle end 6 of the barrel 2. The outside diameter of the cap 46 is precision ground to a diameter equal to that of the section 10. The cap grinding operation references two previously precision ground surfaces, the outside diameters of the chamber 4 and the section 10. A seat 48 is provided in the sleeve 38 to receive the cap 46. When in place over the cap 46 and section 10, the sleeve 38 is substantially incapable of radial movement. When seated on the cap 46, the sleeve 38 is incapable of axial movement. The fully seated sleeve 38 is held in place by a locking collar 34 and dog-nosed screws 36, as shown.

A plug 52 is in the end of the sleeve 38. The plug 52 is an electrical insulator, e.g., nylon or Teflon, and carries and centers the anode 26 in the muzzle 3.

Electrolyte inlet conduits 54 provide electrolyte under pressure to the electrolyte ports 50 in the sleeve 38. In this case, the electrolyte flows upwardly through the bore 3 and out the ports 22. A positive seal is effected between the conduits 54 at the muzzle 6 through annular block 58 and O-ring seals 60.

The plugs 24 and 52 each has conical projections 44 and 56 respectively. The anodes 26 extend through the apex of the respective cones. The cone shaped tips act like baflles to reduce electrolyte turbulence at the inlet and outlet ends of the barrel 2.

An anode electrical lead 62 is also provided at the muzzle-anode-positioner 37. A cathode current lead 64 is attached to the barrel 2 approximately midway between the anode leads 28 and 62.

Rifle barrels generally taper from one end to the other with the narrowest point being at the muzzle. It has therefore been diflicult heretofore to insure the precise central positioning of the anode 26 at the muzzle end of the barrel. By closely fitting the cap 46 about the muzzle 6 and then machining the outside diameter of the cap 46 to correspond to the existing concentric outside diameter of the enlarged section 10, two precise surfaces are provided as guides for radially positioning of the sleeve 38 with respect to the bore 3.

In the particular embodiment of this invention shown in the drawing, the barrel 2, including chamber, bore and muzzle, are simultaneous chromium plated. The barrel comprises a chromium-molybdenum-vanadium steel alloy blank which has initially been gun-drilled and electrochemically machined to an internal diameter of 0.245 inch. An intra-forming operation, produces the rifling in the bore and elongates the blank to a finished length of 20% inches. The lands and grooves of the riding are respectively 0.220 inch and 0.223 inch after intraforming. The outside diameters of the chamber 4 and the section 10 are precision ground to a specified dimension having a surface concentric with the bore 3. The portion of the barrel surrounding the chamber 4 is machined to an outside diameter of 0.980 inch The smaller inside diameter 18 of the sleeve 16 is formed to 0.980 inch The outside diameter of the muzzle cap 46 is precision ground to a tolerance of +0.0o00 -0.0002 Inch and corresponds to that of the section 10. The inside diameter of the bore in the sleeve 38 substantially corresponds to the outside diameter of the cap 46 +0.00o2 -0.0000 mch thereby providing a slip fit relations-hip between the sleeve 38, the cap 46 and the section 10. The anode 26 is a lead-tin coated one-sixteenth inch copper wire drawn to an outside diameter of 0.0762 inch. A conventional chromium plating solution is pumped through the barrel from muzzle to chamber at a rate of about 5 /2 feet per minute. A short reverse etch of about one ampere/in. for about 30 seconds before plating improves adhesion between the chromium and the inside surface of the bore. A short strike of about three amperes/in. for 30 seconds initially coats the bore, especially in the low current density areas andprevents acid attack of the 'bore at the beginning of the plating cycle. Plating itself is accomplished in about 38 minutes at a current density of about two amperes per square inch which produces a deposit thickness of about 0.0005 inch.

While this invention has been disclosed primarily in terms of a single embodiment thereof, it is intended to be limited only to the extent hereinafter set forth.

I claim:

1. A tool adapted to centrally locate an electroplating anode within a small bore rifle barrel having a chamber end with a first predetermined outside diameter, a muzzle end with a second predetermined outside diameter which is less than said first predetermined outside diameter, a bore extending between said chamber and said muzzle and at least one barrel section intermediate said muzzle and said chamber and having a third predetermined outside diameter greater than said second outside diameter, said tool comprising a chamber-'anode-positioner, a muzzle cap, a muzzle-anode-positioner and an anode extending through said muzzle cap and between said positioners, said chamber-anode-positioner comprising a first sleeve having adjoining portions of different internal diameter providing a shoulder for engaging a flange on said barrel, one of said portions having an internal diameter substantially equal to said first predetermined outside diameter and adapted to closely slip over said chamber, electrolyte ports in the other of said portions, a first plug centered in the other of said portions said plug carrying and centering one end of said anode with respect to said chamber, said muzzle cap comprising a hollow cylinder adapted to closely engage said muzzle end and having an outside diameter substantially equal to the diameter of said barrel section, said muzzle-anode-positioner comprising a second sleeve a major portion of which has an internal diameter substantially equal to the outside diameter of said muzzle cap and is adapted to closely engage said cap and said section in a slip-fit fashion, a seat in said sleeve for said cap, electrolyte ports in said sleeve, a second plug centered in said sleeve, said plug carrying and centering the other end of said anode with respect to said muzzle and means for conducting current to said anode.

2. The tool as claimed in claim 1 wherein said plugs have conical tips adjacent said electrolyte ports to reduce electrolyte turbulence during plating.

References Cited UNITED STATES PATENTS 2,425,359 8/ 1947 Zavarella 20426 2,859,157 11/ 1958 Curtiss, Jr. 20426 FOREIGN PATENTS 340,961 6/ 192-9 Great Britain 20426 712,314 7/ 1954 Great Britain 20426 126,030 7/ 1949 Sweden 20426 HOWARD S. WILLIAMS, Primary Examiner T. TUFARI-ELLO, Assistant Examiner U.S. C1. X.R. 

